1. Field of the Invention
The present invention relates to an image recording apparatus for printing a multi-tone image. More particularly, the present invention relates to an image-storage-type image recording apparatus in which image data is stored once before printing. Discussion of the Related Art
A digital image-storing electrophotographic copying apparatus, shown for example in FIG. 15, includes an image input device 200 for reading documents, an image storage device 201 for temporarily storing image data DT read by the image input device 200, and an image printer 202 for performing printing according to an electrophotographic process based on the image data DT stored in the image storage device 201. This type of apparatus can have multiple functions, such as an electronic recirculating document handler function, a reverse output function, a sample copy function, and the like.
In the digital image-storage electrophotographic copying apparatus, the quantity of data (the number of tones) per pixel of the image data DT stored in the image storage device 201 for printing a multi-tone image must be small because of the limited memory capacity of the image storage device 201.
However when the number of tones in the original input image data DT is small, the picture quality in the print output is deteriorated.
To improve picture quality in the conventional apparatus, a pseudo tone generating circuit (hereinafter called "screen generator") 203 is inserted between the image input device 200 and the image storage device 201. The screen generator 203 reduces the number of tones in the image data DT. At the same time, screen generation is made. That is, pseudo tone image data DT' equivalent to the tone characteristic of the actual document image is generated. Subsequently, the pseudo tone image DT' is stored in the image storage device 201. The image printer 202 prints the pseudo tone image data.
In the digital image-storage electrophotographic copying apparatus, the screen generator 203 must match with the image printer 202, because the screen generator 203 substantially corrects the characteristic of the image printer 202.
In the apparatus in which the screen generator 203 is arranged in the side of the image input device 200, another image printer 202', different in speed and function (duplex copy, aftertreatment, etc.) as shown in the drawing, cannot be connected to the image input device 200 and the image storage device 201 used in common. Accordingly, a variation of the apparatus in which a new image printer is connected cannot be accomplished easily. This creates a technical problem in that an image input device 200 having a screen generator 203' matching with the new image printer 202' must be prepared anew.
It is a matter of course that the same problem arises in other image recording apparatus.